Process for manufacturing a charge-balance power diode and an edge-termination structure for a charge-balance semiconductor power device

ABSTRACT

An embodiment of a process for manufacturing a semiconductor power device envisages the steps of: providing a body made of semiconductor material having a first top surface; forming an active region with a first type of conductivity in the proximity of the first top surface and inside an active portion of the body; and forming an edge-termination structure. The edge-termination structure is formed by: a ring region having the first type of conductivity and a first doping level, set within a peripheral edge portion of the body and electrically connected to the active region; and a guard region, having the first type of conductivity and a second doping level, higher than the first doping level, set in the proximity of the first top surface and connecting the active region to the ring region. The process further envisages the steps of: forming a surface layer having the first type of conductivity on the first top surface, also at the peripheral edge portion, in contact with the guard region; and etching the surface layer in order to remove it above the edge portion in such a manner that the etch terminates inside the guard region.

PRIORITY CLAIM

This application claims priority from European patent application No.06425448.5, filed Jun. 28, 2006, which is incorporated herein byreference.

TECHNICAL FIELD

An embodiment of the present invention relates to a process formanufacturing a bipolar power diode comprising charge-balance columnarstructures, and relates to an edge-termination structure for asemiconductor power device, also comprising charge-balance columnarstructures.

BACKGROUND

As is known, in the last few years a wide range of solutions has beendeveloped for increasing the efficiency of semiconductor power devices,in particular in terms of increase in the breakdown voltage and decreasein the output resistance.

For example, U.S. Pat. Nos. 6,586,798, 6,228,719, 6,300,171 and6,404,010, which are incorporated by reference, describevertical-conduction semiconductor power devices, in which columnarstructures of opposite conductivity are formed inside an epitaxiallayer, forming part of a drain region having a given type ofconductivity. The columnar structures have a dopant concentration whichis substantially the same as, and of a type opposite to, the dopantconcentration of the epitaxial layer in such a way as to provide asubstantial charge balance (the so-called “Multi Drain (MD)technology”). The charge balance enables high breakdown voltages to beobtained, and moreover the high dopant concentration of the epitaxiallayer enables a low output resistance (and low losses in conduction) tobe achieved.

In brief, the formation of the aforesaid columnar structures envisages asequence of steps of growth of N-type epitaxial layers, each step beingfollowed by a step of implantation of a P-type dopant. The implantedregions are stacked so as to form the columnar structures. Next, bodyregions of the power device are formed in contact with the columnarstructures, in such a manner that the columnar structures constitute anextension of the body regions into the drain region.

The evolution of this technology has witnessed a progressive increase inthe density of the elementary strips forming the devices, for furtherincreasing the charge concentration in the epitaxial layer and obtainingdevices that, given the same breakdown voltage (which is substantiallyrelated to the height of the columnar structures), have a lower outputresistance. On the other hand, however, the increase in the density ofthe elementary strips has led to a reduction of the thermal budget ofthe devices and a corresponding increase in the number of steps ofepitaxial growth, and accordingly to an increase in the manufacturingcosts and times, and in the defectiveness intrinsically linked toepitaxial growth.

Alternative technologies have consequently been developed to obtaincharge-balance columnar structures; these technologies envisage, forexample, formation of trenches inside the epitaxial layer and subsequentfilling of the trenches with semiconductor material appropriately dopedto obtain the charge balance.

For instance, in co-pending patent applications WO-PCTIT0600244, filedon Apr. 11, 2006, and WO-PCTIT0600273, filed on Apr. 21, 2006, both inthe name of the present applicant and incorporated by reference,improved techniques (which will in part be referred to in what follows)have been described for the formation of trenches and their filling, inparticular substantially free from residual defectiveness, to obtaincharge-balance structures, and for the formation of semiconductor powerdevices provided with the charge-balance structures. In particular, inWO-PCTIT0600273 a non-selective epitaxial growth inside the trenches isproposed, also affecting a top surface of the layer in which thetrenches are formed. Consequently, at the end of the epitaxial process awrinkled surface layer made of semiconductor material may be formed,characterized by the presence of a plurality of grooves in areascorresponding to the columnar structures. It is also proposed to formthe power devices at least in part inside this wrinkled surface layer.

Furthermore, as is known, the provision of efficient edge-terminationstructures is a key point for ensuring proper operation of powerdevices; in fact, it is in the edge areas that the largest number ofbreakdowns occur on account of the concentration of the electrical fieldlines due to the curvature of the edge regions. The edge terminationshave the function of locally reducing the intensity of the electricalfield so as to prevent peaks of intensity at the edges.

So far, the problem of providing edge-termination structures forcharge-balance power devices, which enable maximization of theperformance in reverse biasing of said devices, has not yet been solvedin a satisfactory way for all applications.

SUMMARY

One or more embodiments of the present invention further improve thetechniques for producing charge-balance power devices, in particular forthe producing a bipolar power diode, and are directed to an efficientedge-termination structure for the aforesaid devices, based upon thepower diode.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention are now described, purely byway of non-limiting example and with reference to the drawings, wherein:

FIG. 1 shows a cross section through a wafer made of semiconductormaterial in an initial step of a manufacturing process of a power diodeand of a corresponding edge-termination structure, according to a firstembodiment of the present invention;

FIG. 2 shows a top plan view of the wafer of FIG. 1 in a subsequent stepof the manufacturing process;

FIGS. 3 to 10 show cross sections through the wafer of semiconductormaterial along the line of section III-III of FIG. 2, in subsequentsteps of the manufacturing process;

FIG. 11 shows a top plan view of a wafer of semiconductor materialsimilar to that of FIG. 2, corresponding to an embodiment of the presentinvention;

FIGS. 12 and 13 show cross sections through the wafer of semiconductormaterial along the line of section XII-XII of FIG. 11 in an initial stepand in a final step of the manufacturing process, respectively;

FIGS. 14 a-14 f show cross sections of a wafer of semiconductor materialin successive steps of a manufacturing process of a semiconductor powerdevice, in particular a MOSFET, and of a corresponding edge-terminationstructure in accordance with a second embodiment of the invention; and

FIGS. 15 a-15 e show cross sections of a wafer of semiconductor materialin successive steps of a manufacturing process of a semiconductor powerdevice and of a corresponding edge-termination structure in accordancewith a third embodiment of the invention.

DETAILED DESCRIPTION

A process for manufacturing a semiconductor power diode withcharge-balance techniques is now described according to one or moreembodiments of the invention. As will be clarified hereinafter, thestructure that is obtained can be used, with the appropriatemodifications, to obtain an edge structure for a generic charge-balancepower device (for example, a MOSFET, a BJT, etc.).

FIG. 1 shows a wafer 1 made of semiconductor material, typicallysilicon, comprising a substrate 2 having a first type of conductivity,for example of an N⁺⁺ type with resistivity lower than 10 mΩ·cm, and anepitaxial layer 3, also having the first type of conductivity, forexample of an N type with resistivity of between 0.1 Ω·cm and 2 Ω·cm.The wafer 1 has, for example, surface orientation <100>, and theepitaxial layer 3 has a top surface 3 a.

In an initial step of the manufacturing process (FIGS. 2 and 3), a firstimplantation is performed of dopant atoms with a second type ofconductivity, in the example a P-type conductivity (with boron atoms),to form a first doped region 4 in the proximity of the top surface 3 aof the epitaxial layer 3. As will be clarified hereinafter, the firstdoped region 4 is to form an anode region of a power diode, and part ofa corresponding edge-termination structure (in particular a guard ring).In detail, an implantation is performed with high dose (of between5·10¹³ and 3·10¹⁵ at/cm²) and medium energy (of between 80 and 160 keV),through a first mask (not illustrated) of appropriate shape, so as tolocalize the implantation in an active area of the power device and in aperimetral region of the same active area (at the boundary with acorresponding edge region). For example, the first doped region 4 has inplan view a closed generally rectangular shape (as may be seen in FIG.2).

A second implantation of dopant atoms of a P type is then performedthrough a second mask (not illustrated) to form a ring region 5 of theedge-termination structure of the power device. The implantation, whichin the example is also performed with boron atoms, is at a low dose (ofbetween 5·10¹¹ and 8·10¹² at/cm²) and high energy (of between 120 keVand 1 MeV). It follows that the ring region 5 is set at a depth lowerthan that of the first doped region 4 with respect to the top surface 3a of the epitaxial layer 3. In particular, the second mask locates thering region 5 in the perimetral region of the power device. In detail,the ring region 5 completely surrounds the first doped region 4 and hasan area of overlapping 6 with the latter (indicated by the dashed line).It is consequently possible to distinguish in the wafer 1 an active area1 a, which is designed for providing active devices (in the example thepower diode), and set in which is an active portion 4 a of the firstdoped region 4; and an edge area 1 b, which is designed for providing anedge-termination structure, and set in which are an edge portion 4 b ofthe first doped region 4, and the ring region 5.

Next (FIG. 4), charge-balance columnar structures 7 are formed throughthe epitaxial layer 3, and accordingly also through the alreadyimplanted regions, i.e., the first doped region 4 and the ring region 5,substantially as described in detail in the aforesaid co-pending patentapplications WO-PCTIT0600244, and WO-PCTIT0600273.

In summary, the process for the formation of the columnar structures 7envisages first the formation, by means of anisotropic dry etchingthrough an appropriate masking, of deep trenches 8 inside the epitaxiallayer 3 (and through the first doped region 4 and the ring region 5).The deep trenches 8 have, for example, a width, at the level of the topsurface 3 a, of between 0.8 and 2 μm and a smaller width at their bottomof between 0.2 and 1.4 μm. In addition, the height of the deep trenches8 varies, for example, between 5 and 50 μm and determines, together withthe thickness of the epitaxial layer 3, the voltage class of the finaldevice (by way of example, corresponding to a height of 5 μm is avoltage class of 100 V, whereas corresponding to a height of 30 μm is avoltage class of 600 V). Then, the wafer 1 is subjected to an annealingtreatment in a hydrogen environment at a temperature of 1000-1150° C.for a treatment time of 1-15 min. This treatment, in addition toeliminating the damage due to the preceding etching, leads to exposure,on the bottom of the deep trenches 8 of the crystallographic planes<100> and <130> and, along the side walls of the plane <010> (the deeptrenches 8 consequently assume the shape visible in FIG. 4). Next, thedeep trenches 8 are filled via epitaxial growth with silicon doped withthe second type of conductivity, in one example of a P type with boronions. In particular, the epitaxial growth occurs by supplying a flow ofa gas containing silicon (for example, dichlorosilane) and of a gascontaining boron (for example, diborane), and the doping control isensured by maintaining a constant gradient of growth in the flow ofdiborane (for example, by setting a linear ramp increasing between aninitial flow and a final flow of a value twice that of the initial one),and maintaining the flow of dichlorosilane constant. Given that thegrowth is not selective with respect to the deep trenches 8, theepitaxial growth is performed both inside the trenches, starting fromthe side walls, with a faster rate in the proximity of the surface, andoutside the trenches, in particular on the top surface 3 a of theepitaxial layer 3. In order to prevent premature closing of the deeptrenches 8 because of the encounter of the fronts of growth from thewalls, successive steps are alternated of epitaxial growth and etching,for example with HCl, of the portions of surface growth (the so-called“multi-step” process). At the end of this process sequence, thestructure shown in FIG. 4 is obtained, with the formation of thecolumnar structures 7, which completely fill the deep trenches 8 andhave a uniform doping spatial distribution and reduced presence ofdefects (for example, voids). The process of non-selective epitaxialgrowth also affects the top surface 3 a of the epitaxial layer 3, on topof which a wrinkled surface layer 9 of a P type is formed, with groovesin areas corresponding to the columnar structures 7. In particular, eachcolumnar structure 7 has a surface extension 10 at and on the topsurface 3 a having a non-planar surface pattern and a characteristicgrooved, in particular V-shaped, cross section. Connection portions 11of the wrinkled surface layer 9, having a planar surface pattern,connect the surface extensions 10 of adjacent columnar structures 7.

According to an embodiment of the present invention (FIG. 5), a furtherphototechnique (which comprises a masking and a subsequent etching) isthen carried out to eliminate a portion of the wrinkled surface layer 9in a position corresponding to the edge region 1 b, or in an equivalentway to the ring region 5. The etch also involves a surface portion ofthe epitaxial layer 3 so that the surface of the epitaxial layer abovethe ring region 5 is planarized and is at a lower level with respect tothe active area 1 a of the device (in which the wrinkled surface layer 9remains). Consequently, above the ring region 5 a planar surface 3 b isdefined, set at a lower level with respect to the top surface 3 a of theoriginal epitaxial layer 3.

The aforesaid etch involves also part of the first doped region 4 in aposition corresponding to the area of overlapping 6 and is calibrated insuch a manner as to stop inside the same doped region, thus forming astep 13 inside its edge portion 4 b. This step 13 connects the topsurface 3 a with the planar surface 3 b, and is set around the entireactive area 1 a of the power device. Equivalently, the first dopedregion 4 has a given thickness at its active portion 4 a, and a smallerthickness at an end area of its edge portion 4 b, beyond the step 13.

The fact that the etch step terminates at the first doped region 4(having a high doping level) improves the stability of the breakdown ofthe power device, preventing dangerous concentrations of the electricalfield lines.

In fact, in reverse biasing, the electrical field lines are not able toreach the sharp edge of the etch, which is protected by the P⁺ junction.Basically, the edge portion 4 b of the first doped region 4, in additionto electrically connecting the ring region 5 to an active region of thepower device, represents a guard ring for the power device, whichenables prevention of undesirable effects (in terms of concentration ofelectrical field) of the step resulting from etching of the wrinkledsurface layer.

Next, FIG. 6, a field-oxide layer 15 is grown on top of the wafer 1, andthe active area 1 a is defined by etching the field-oxide layer 15 onthe active area 1 a. The field oxide consequently remains only on theedge area 1 b, and in particular on the edge portion 4 b of the firstdoped region 4 (in which it has the non-planar surface pattern of theunderlying wrinkled surface layer 9), and on the ring region 5 (in whichit has, instead, a planar surface pattern at a lower level). The thermalprocess linked to the field oxide growth (at the expense of the exposedsilicon) also causes an extension of the previously implanted regions.In particular, the ring region 5 extends as far as the planarizedsurface 3 b, and joins an end part of the edge portion 4 b.

The manufacturing process of the power diode then proceeds with anenrichment implantation in the active area 1 a of a P type (for example,once again with boron atoms), with an implantation dose of between1·10¹³ and 5·10¹⁴ at/cm² and energy of between 80 and 200 keV, in orderto provide an enrichment region 16 in a surface portion of the wafer(and in particular inside the wrinkled surface layer 9) (FIG. 7). Theenrichment region 16 has the function of improving a contact that willbe subsequently formed at the anode region of the power diode. Theimplantation can possibly be carried out through an appropriatesacrificial-oxide layer previously deposited in the active area(ion-pre-implantation oxide). There follows in any case a thermaldiffusion process.

Next (FIG. 8), at an outer periphery of the device, beyond the edge area1 b (for example, at the points of cutting of the wafer to define dicecontaining the power devices), a second doped region 18, of a N⁺⁺ typeat high dosage, is formed in the proximity of the surface of the wafer(the planarized surface 3 b). In detail, an appropriate implantationmask 19 is first formed, coating both the active area 1 a and the edgearea 1 b, leaving only the aforesaid periphery of the device exposed.Then the insulating layer 15 is etched, and the second doped region 18is implanted. In particular, the second doped region 18 has the functionof bringing to the surface the cathode potential of the power diode (thecathode being constituted by the epitaxial layer 3) so as to limit thelines of the electrical field horizontally in reverse biasing. Next, theimplantation mask 19 is removed from the wafer, and the second dopedregion 18 is activated.

There follows (FIG. 9) a sputtering process to form a frontmetallization layer 20 on the wafer, the thickness of which depends uponthe current-carrying capacity that it is intended to specify for thedevice. The front metallization layer 20 is then etched so as to definea first contact region 20 a for the anode (in contact with theenrichment region 16), and a second contact region 20 b for the cathodeof the diode (in contact with the second doped region 18).

A passivation layer 22 is then deposited on the wafer (FIG. 10) and nextit is defined via an appropriate masking so as to open contact windowsfor the first and second contact regions 20 a, 20 b. The processterminates with finishing of the back (of a known type), and cutting ofthe wafer to obtain the various dice containing the power devices.

According to a second embodiment of the present invention (FIGS. 11 and12), the first doped region 4 has, in the active area 1 a, a strip-likeconfiguration. In this case, the active portion 4 a is formed by aplurality of strips extending all in a same direction, parallel to oneanother. The strips, in the edge area 1 b, are connected to the edgeportion 4 b, which once again overlaps the ring region 5 at the area ofoverlapping 6.

The manufacturing process of the power diode is substantially equivalentto what has been previously described, with the difference that theactive portion 4 a is not continuous, and a charge-balance columnarstructure 7 is located inside each strip. Shown in FIG. 13 is theresulting structure at the end of the process, in which thecharacteristic edge-termination structure may be recognized, comprisingthe edge portion 4 b of the first doped region 4, in which the step 13due to etching of the wrinkled surface layer 9 is located, and the ringregion 5. Also in this case, the final structure has a differentlevel/plane for the active anode region and the edge-termination region,which are connected by the step 13.

The diode edge-termination structure previously described can be usedfor a generic charge-balance power device, for example a MOSFET. Themanufacturing process of a charge-balance MOSFET is described in detailin the aforesaid copending patent application WO-PCTIT0600273, and ishereinafter briefly presented, in two variants, showing its integrationwith the described edge-termination structure. In both cases, the MOSFETis formed on a non-planar surface partially inside the wrinkled surfacelayer 9, exploiting portions of said layer, in particular the surfaceextensions 10 of the columnar structures 7, as active areas of thedevice.

A first variant initially envisages (FIG. 14 a) execution, in the activearea, of a surface implant, of an N type with low energy, to form asurface-implantation layer 24 in the proximity of the top surface 3 a ofthe epitaxial layer 3. The implantation is made prior to the formationof the columnar structures 7 and, for example, after the formation ofthe first doped region 4 and of the ring region 5 in the edge area 1 b.It should be noted that, in this case, the first doped region 4 does notextend in the active area and comprises only the edge portion 4 b.

The process proceeds with the steps described previously in

FIGS. 4 to 6, concerning the edge-termination structure, namely, withformation of the columnar structures 7, etching of the wrinkled surfacelayer 9 in the edge area 1 b and consequent definition of the step 13,and formation of the field-oxide layer 15.

Next (FIG. 14 b, showing an enlarged portion of the active area, towhich the subsequent process steps refer), in a surface region of theconnection portions 11, between adjacent surface extensions 10 of thecolumnar structures 7, N-type implantations are carried out to formsurface contact regions 25.

This is followed (FIG. 14 c) by a thermal diffusion process fordefinition of sinkers 26 of an N type, which reverse the conductivity ofthe respective connection portions 11 and reach the underlyingsurface-implantation layer 24, also of an N type. On the wafer, onceagain limitedly to the active area, a gate-oxide layer 27 is then grown,on top of which a polysilicon layer is deposited and subsequently etchedso as to obtain gate regions 28 at the top of the sinkers 26.

Next (FIG. 14 d), a P-type body implantation is carried out, through thegate-oxide layer 27 and exploiting the gate regions 28 as “hard mask”,which is followed by a thermal diffusion process, to form body regions29. The latter extend inside the surface extensions 10 of the columnarstructures 7, consequently reproducing the non-planar profile thereofwith grooved cross section, and partially inside the sinkers 26 beneaththe gate regions 28 (where they form channel regions of the transistor).

A P⁺⁺-type deep-body implantation is then carried out (FIG. 14 e),having, for example, the same characteristics (in terms of energy anddose) as those of the implantation leading to formation of the firstdoped region 4. This is followed by a thermal diffusion process to formdeep-body regions 30 in a central area of the surface extensions 10.Next, a N⁺-type source implantation is carried out to form sourceregions 32 inside the body regions 29 and deep-body regions 30. This isfollowed by a process of deposition and definition of a dielectric layerto form insulating regions 33 on the gate regions 28, and opening ofcontacts. At the end of the manufacturing process, a power MOStransistor is consequently obtained on a non-planar surface, with a gateoxide and gate region in a planar area and a body region in a non-planararea (in particular made inside the surface extension of acharge-balance columnar structure).

FIG. 14 f shows the final structure of the MOSFET with the correspondingedge structure, obtained with final steps of formation of the seconddoped region 18 for the cathode contact, of metallization, and ofpassivation, in a way similar to what has been described previously. Inparticular, the deep-body region 30 of the last active cell (or stripe)of the transistor is connected to the edge portion 4 b of the firstdoped region 4 (anode of the diode of the edge termination).

A second variant of the manufacturing process of a charge-balance MOSFETinitially envisages the process steps described with reference to FIGS.3 to 6 concerning the edge-termination structure, namely, with formationof the edge portion 4 b of the first doped region 4 (which once againdoes not extend into the active area) and of the ring region 5;formation of the columnar structures 7; etching of the wrinkled surfacelayer 9 in the edge area 1 b and consequent definition of the step 13;and formation of the field-oxide layer 15.

In the active area, a P-type surface implantation is then performed toform a body layer 35 (FIG. 15 a), which extends within a surface portionof the wrinkled surface layer 9. Next, an N-type blanket implantation isperformed on the surface of the wafer 1 (once again in the active area),to form a source layer 36, which is located in a surface portion of thebody layer 35.

A deep implantation is then carried out to form deep-body regions,designated once again by 30, at the surface extensions of first columnarstructures, and not in second columnar structures that alternate to thefirst columnar structures inside the epitaxial layer 3 (FIG. 15 b).Next, in the connection portions 11 of the wrinkled surface layer 9surface trenches 37 are opened, which traverse the connection portions11 and reach the underlying epitaxial layer 3. The surface trenches 37define body regions 29 of the transistor.

In the active area, a gate-oxide layer 38 is then grown on the wafer 1(FIG. 15 c), deposited on top of which is a polysilicon layer 39, of aconformable type, which fills the surface trenches 37.

The polysilicon layer is then etched so as to obtain gate regions 28 inareas corresponding to the surface trenches 37 (FIG. 15 d). This isfollowed by a process of deposition of a dielectric layer to forminsulating regions 33 on the gate regions 28, and opening of thecontacts. At the end of the manufacturing process a power MOSFET isconsequently obtained on a non-planar surface, with oxide and channelregions in an area defined by a trench-formation process. In particular,the channel region extends vertically inside the body layer 35 betweenthe source layer 36 and the epitaxial layer 3, at the sides of thesurface trenches 37. The body region is in a non-planar area, inside thesurface extension of a charge-balance columnar structure.

Shown in FIG. 15 e is the final structure of the MOSFET with thecorresponding edge structure, made with final steps of formation of thesecond doped region 18 for the cathode contact, metallization, andpassivation, in a way similar to what has been described previously. Inparticular, the body region 29 of the last active cell (or stripe) ofthe transistor is connected to the edge portion 4 b of theedge-termination structure.

Advantages of the described manufacturing process and of the resultingstructures are clear from the foregoing description.

First, the process enables a charge-balance power diode and acorresponding efficient edge-termination structure to be obtained, whichenables maximization of the performance in reverse biasing of thedevice.

The edge-termination structure can be easily integrated in power devices(for example, MOSFETs) based upon the charge-balance concept. Inparticular, the process described envisages removal in the edge area ofthe wrinkled surface layer that is formed after the formation of thecharge-balance columnar structures, and the etching for this removal iscalibrated so as to terminate inside a heavily doped region (the edgeportion 4 b of the first doped region 4), which represents a guardregion against the concentrations of electrical field. The same heavilydoped region connects an active region of the power device (for examplean anode region in the case of the diode, or else a body region in thecase of the MOSFET) with a ring region of the edge-terminationstructure. The resulting structure is consequently extremely efficientand enables prevention of breakdown phenomena of the power device (whichcan have a cut-off voltage that can even reach 1500 V, according to thethickness of the epitaxial layer).

Finally, it is clear that modifications and variations can be made towhat is described and illustrated herein, without thereby departing fromthe scope of the present invention.

In particular, it is clear that, applying the concepts described, it ispossible to obtain different power devices, for example an IGBT(insulated-gate bipolar transistor), a BJT, or a Schottky diode.

Furthermore, the possibility of obtaining dual structures, in which thecharge balance is achieved by means of formation of N-doped columnarstructures in a P-doped epitaxial layer is evident.

The columnar structures 7 may extend throughout the thickness of theepitaxial layer 3, terminating inside the substrate 2. As furtheralternative, a buffer layer, for example of an N type, can be providedbetween the substrate 2 and the epitaxial layer 3, and the columnarstructures 7 may terminate in the buffer layer.

Furthermore, the concepts underlying the described process may beapplied in a generic power device, in which it is provided, on the topsurface of the wafer, a doped surface layer extending also in the edgearea, envisaging etching and removal of said layer at the edge area,stopping the etching inside a heavily doped guard region, in order tolimit breakdown phenomena.

A device formed according to an above-described process or otherwisehaving the above-described structure may be part of a circuit, such as apower supply, and the circuit may be part of a system, such as acomputer system.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention.

1. A process for manufacturing a semiconductor power device, comprising:providing a body made of semiconductor material having a first topsurface; forming an active region with a first type of conductivity inthe proximity of said first top surface and inside an active portion ofsaid body; and forming an edge-termination structure, comprising a ringregion having said first type of conductivity and a first doping level,set within a peripheral edge portion of said body and electricallyconnected to said active region, wherein said step of forming anedge-termination structure further comprises forming a guard region,having said first type of conductivity and a second doping level, higherthan said first doping level, in the proximity of said first top surfaceand connecting said active region to said ring region; and in that itfurther comprises: forming a surface layer having said first type ofconductivity on said first top surface, also at said peripheral edgeportion, in contact with said guard region; and etching said surfacelayer in order to remove it above said edge portion in such a mannerthat the etch terminates inside said guard region.
 2. The processaccording to claim 1, wherein said step of etching said surface layerfurther comprises etching a surface portion of said body in such amanner that said body has, at said peripheral edge portion, a second topsurface set at a lower level with respect to said first top surface, andthat a step is thus formed inside said guard region, connecting saidfirst and second top surfaces.
 3. The process according to claim 2,wherein said step of etching a surface portion of said body (3)comprises planarizing said second top surface (3 b).
 4. The processaccording to claim 2, wherein forming said active region comprisesarranging said active region in such a manner that it extends as far asa first level, at least corresponding to said first top surface, andforming said ring region comprises arranging said ring region in such amanner that it extends as far as a second level, lower than said firstlevel and corresponding to said second top surface.
 5. The processaccording to claim 4, wherein arranging said ring region comprises:introducing dopant species of said second type of conductivity insidesaid body at a distance of separation from said first top surface, priorto said step of etching said surface layer; and causing a process ofdisplacement of said ring region as far as said second top surface aftersaid step of etching said surface layer.
 6. The process according toclaim 5, further comprising the steps of growing a thermal-oxide layerabove said body after said step of etching said surface layer, andremoving said thermal-oxide layer above said active portion; said stepof growing a thermal-oxide layer comprising said step of causing aprocess of displacement of said ring region.
 7. The process according toclaim 1, wherein said body has a second type of conductivity, oppositeto said first type of conductivity; further comprising the step offorming charge-balance columnar regions having said first type ofconductivity through said body, both in said active portion and in saidedge portion, and in particular through said guard region and said ringregion; said step of forming columnar regions further comprising formingsaid surface layer and in particular surface extensions of said columnarregions on said first top surface and connection portions between saidsurface extensions.
 8. The process according to claim 7, wherein saidsurface layer has a non-planar profile, and said surface extensions havea grooved, in particular substantially V-shaped, surface profile.
 9. Theprocess according to claim 7, wherein forming columnar regionscomprises: forming deep trenches inside said body; and filling said deeptrenches with semiconductor material via non-selective epitaxial growthso as to form said columnar regions inside said deep trenches and saidsurface extensions on said first top surface; said columnar regionshaving a doping level such as to substantially balance an oppositedoping level of said body.
 10. The process according to claim 9, whereinfilling said deep trenches comprises supplying a gas containing saidsemiconductor material and a gas containing dopant ions of said firsttype of conductivity; supplying comprising varying, in particularincreasing, a flow of said gas containing dopant ions.
 11. The processaccording to claim 7, wherein said power device is a bipolar diode, andwherein said active region has in plan view a substantially rectangularshape and is surrounded by said ring region; a peripheral portion ofsaid active region being connected in a continuous way to said guardregion, and said columnar regions moreover traversing said activeregion.
 12. The process according to claim 7, wherein said power deviceis a bipolar diode, and wherein said active region has in plan view theshape of parallel strips, and is surrounded by said ring region;peripheral strips of said active region being connected to said guardregion, and said columnar regions each traversing a respective one ofsaid strips.
 13. The process according to claim 7, wherein said powerdevice is a MOS device, and said active region comprises a plurality ofbody regions, each formed at least partially inside a respective surfaceextension of said columnar regions; further comprising forming gatestructures between adjacent columnar regions, at least in part abovesaid first top surface, and forming source regions of said second typeof conductivity inside said body regions; the step of removing saidconnection portions in order to separate from one another said surfaceextensions and interrupting said wrinkled surface layer being moreoverenvisaged prior to formation of said gate structures.
 14. The processaccording to claim 1, wherein said body has a second type ofconductivity, opposite to said first type of conductivity, and saidguard region forms with said body a bipolar diode, of which said guardregion is the anode and said body is the cathode; further comprisingforming, in a surface portion of said body, distinct from said activeportion and from said edge portion, a contact region having said secondtype of conductivity, for contacting said cathode. 15-43. (canceled)